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Figure 3. Rainfall and mean temperature recorded at the camp site (Forestry Station Ampijoroa) from November 1995 through August 1997. Black and diagonal hatching indicate periods of water surplus, stippling water deficit (Brower et al. 1997).

rainy season, and 1746mm in the 1996-97 rainy season. Annual rainfall in 1996 (January to December) was 1775 mm. About 60% of rain falls during the night (based on Donque, 1975:427) making continuous observations of nocturnal primates more difficult.

Mean average monthly temperature ranged between 22°C in July and 28°C in November. The highest mean maximum monthly temperature was recorded in November (35°C) and the lowest mean minimum monthly temperature in July (15°C).

Forest. Forest characterization with plant species lists has been reported in detail in Thalmann (2001:296 ff.), and is shortly summarized here. From the plot data it has been extrapolated that 6120 trees/ha with a DBH > 2 cm of 87 species and 2520 woody lianas/ha (20 species) with a DBH > 1 cm constitute the major plant biomass in the forest. Eleven tree species and two woody liana species not represented in the plots were additionally used as food species by either Avahi or Lepilemur, as was 1 nonwoody liana by Avahi. The plot samples with additional data from observations reasonably represent the forest for specific richness estimated with jackknife methods (Krebs, 1998; 95% estimate: 96-113 tree species, 21-29 liana species).

Correlations between phenology expressed in terms of number of trees per species and TCV are, with the exception of available fruit, positive and significant. This might lead to the use of tree number per species as proxy for available food. This is inadequate as the correlation between rain data and phenology shows a different pattern. The phenology in terms of TCV is more suitable for further considerations (see below).

Correlations of Environmental Variables

Climate. There is a significant positive correlation between the amount of rain and the mean temperature (r = 0.59, p <0.05). The correlation is not very high, hence, the climate is rather moderately variable in terms of temperature over the year, and the major climatic variable is obviously the amount of rain.

Climate and Phenology (Table 1). As pointed out above, correlations of climate and phenology are most appropriate between rainfall and TCV, with rainfall as the major climatic variable and TCV as best proxy for forest composition and, hence, food availability in general. Surprisingly, results show that correlations between rainfall and potentially preferred food items of folivores such as sprouting buds, sprouting leaves, young leaves, and flowers are not significant (Table 1). This indicates that volume availability of these items depend on more than rainfall, and that accordingly a certain amount of plant items (e.g., young leaves) are available throughout the entire year (Figure 2). However, the major increase occurs after the first substantial rains at the beginning of the rainy season.

Table 1. Correlations between rain and phenology data in terms of tree crown volume: Spearman rank correlations

Phenology

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Flo

Fr

Rain

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